Begining Circuit Analysis and Ohms Law Page 3
Resistance
There is one more thing that we need to talk about when we are talking about voltage and current. We need to talk about Resistance. Generally the term resistance is applied to all electrical components that are not batteries. With the circuit we've been using in this guide there is only one component that is not a battery. The light bulb in this circuit is the only component that is not a battery.
A light bulb has a set amount of resistance.
All light bulbs have a set amount of resistance that is built in to them. This resistance does not change through out the bulbs life (until it stops working, when it becomes an open circuit). The amount of resistance in the bulb is directly related to how bright it gets. Resistance is measured in Ohms.
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What is being measured
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How it is measured
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Distance
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Inches
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Distance
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Centimeters
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Voltage Potential
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Volts
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Current
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Amps
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Resistance
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Ohms
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You can see from the table above that Resistance is measured in Ohms.
Back to The Water Analogy
Looking back at the water analogy, the amount of water in the lake is the same as voltage in a battery, while the amount of water flowing out of the lake is the same as the current in a circuit. Now we can add that the size of the opening in the dam for water to come out is the same as the resistance in a circuit. In other words:
Resistors limit the current, or flow, in a circuit.
Resistors resist, or restric the flow of electricity in a circuit. Now that we understand Voltage, Current and Resistance, we are ready to learn Ohms Law which relates all three of them together.
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